Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$88.27	13.532%	$100.2147	$100.21	$100.20	$100.20
Purchase #2	$206.78	11.304%	$230.1544	$230.15	$230.15	$230.20
Purchase #3	$29.56	7.518%	$31.7823	$31.78	$31.80	$31.80
Purchase #4	$233.71	10.621%	$258.5323	$258.53	$258.55	$258.50
Purchase #5	$144.82	3.842%	$150.384	$150.38	$150.40	$150.40
Purchase #6	$173.75	10.391%	$191.8044	$191.80	$191.80	$191.80
Purchase #7	$72.77	4.770%	$76.2411	$76.24	$76.25	$76.20
7 purchase totals =	$949.66		$1,039.1132	$1,039.09	$1,039.15	$1,039.10